Proper tonicities of fixing fluids for scanning electron microscopy of delicate chick embryos have been determined. The work will be extended to the study of microappendages by freeze fracturing technique in an attempt to determine what, if any, changes in membrane structure may be responsible for the pleomorphism so well known in microappendages. BIBLIOGRAPHIC REFERENCES: Litke, L.L. and F.N. Low 1977. Fixative tonicity for scanning electron microscopy of delicate chick embryos. Am. J. Anat., 148:121-127. Merchant, R.E. and F.N. Low 1977. Identification of challenged subarachnoid free cells. Am. J. Anat., 148:143-148.